Starting May 1 (and for a limited time), if you bring a smartphone that’s less than three years old and still in “good, working condition” into an AT&T store, you can get $100 or more to use toward the purchase of a new phone.

Some day, you’ll never have to worry about whether you left the lights on, the garage door open or the curling iron plugged in, because you’ll be able to control it all remotely by phone or tablet. AT&T is offering a taste of …